This invention relates to directional couplers having plural, independent coupled outputs.
Waveguide is a form of transmission line in the form of a hollow pipe through which electromagnetic energy can propagate. Waveguide is advantageous because of its relatively low loss and high power-handling capbbility, and finds extensive use at microwave (3-30 GHz) and millimeter-wave frequencies (30-300 GHz). Waveguide can be used at frequencies lower than microwave frequencies, but tends to be relatively large and heavy, so that other forms of transmission line may be preferable.
In electromagnetic communication systems, there is often a need to sample a particular proportion of energy flowing in a transmission line, and to couple the sample into another transmission line. This may be accomplished in many ways, but a particularly advantageous arrangement is known as a directional coupler. A directional coupler includes two coupled transmission lines arranged so that energy flowing in one direction in one transmission line couples so as to flow in a preferred direction in the other transmission line. Reversal of the direction of energy flow in one transmission line results in a reversal of the direction of flow in the other transmission line.
In rectangular waveguide energy propagation systems, a directional coupler may be implemented by paralleling two rectangular waveguides with a common broad wall, and forming coupling apertures in the common wall in such a fashion that signal flowing through the coupling apertures adds in-phase in one direction and cancels in the other direction. The conditions under which this occurs are well known in the art and no further description is required. Another type of waveguide directional coupler includes two parallel, spaced-apart waveguides with branch waveguides extending therebetween. Such a directional coupler is described in U.S. patent application Ser. No. 842,773, filed Mar. 21, 1986, in the name of Praba et al, now U.S. Pat. No. 4,679,011. In some embodiments, the Praba et al. arrangement uses waveguides having cross-sectional dimensions which have reduced height compared with standard waveguide, for increased bandwidth. Tapered adaptors allow coupling of the reduced-height waveguides of the directional coupler to standard waveguides.
In some systems applications, it is advantageous to use more than one directional coupler. When many directional couplers are needed, their combined physical size and weight may be disadvantageous, especially if tapered adaptors are used between couplers. It would be advantageous to reduce the overall size of arrangements of plural directional couplers.